Solutions containing six different concentrations of Cd equilibrated with ten alkaline-calcareous surface soils showed that Cd adsorption fitted the Langmuir isotherm. Where the amount of Cd absorbd is ‘xlm’ and the solution concentration at equilibruim is ‘C’, simple correlation coefficients relating six pairs of C/x/m and ‘C’ for each soil, averaged 0.953. The CaCO3 content of the soil was the major determinant of strength of Cd adsorption as evidenced through a positive significant correlation coefficient (r = 0.86**) between calculated adsorption maxima and CaCO3 content. Using the linear stepwise regression technique, it was observed that 85 per cent of the variations in adsorption maxima was due to the combined effect of pH, CaCO3, organic carbon and clay contents.
Langmuir isotherm, adsorption, cadmium, alkaline and calcareous soils
